This invention relates generally to electric motors and more particularly, to seal rings for air cooled electric motors with rotor mounted cooling fans.
Known electric motors typically include a motor housing, a stator, and a rotor assembly. The rotor assembly includes a rotor core and a rotor shaft extending through the core. The housing includes a shell and two endshields and houses at least a portion of the rotor assembly. Electric motors also include at least one bearing sized to receive the rotor shaft. Typically the bearings are coupled to the endshields with brackets or other mountings. The endshields attach to ends of the frame housing shell.
For reliable performance, most large electric motors include internal fans mounted on the rotor shaft to cool the motor windings. The fans move cooling air past the stator windings to prevent winding failures and to increase the life and reliability of the motor. Known large electric motors include a gap or clearance between the fan and a mating air deflector to allow for manufacturing variations. This clearance between the fan and the air deflector has a disadvantage of permitting air to recirculate and thus reduce the cooling air to the stator windings. Additionally in large electric motors that include air coolers, air recirculated between the gap or clearance between the air deflector and the fan does not pass through the air cooler which raises the temperature of the cooling air and thus providing less cooling to the stator windings. Further, failures and major maintenance of large electric motors, such as nuclear reactor recirculation pump motors, in plants have a large impact on plant operating costs and maintenance costs.
It would be desirable to provide an electric motor with reduced cooling air recirculation and increased cooling of motor windings to prevent motor failures and increase motor reliability.
An electric motor cooling fan having a seal ring reduces cooling air recirculation inside the motor which increases the cooling of motor windings for the prevention of motor failures and increases motor reliability. The cooling fan includes two opposed, spaced apart, and substantially circular fan shrouds. A plurality of fan blades extend between and are attached to the fan shrouds. The fan blades are spaced circumferentially around the fan shrouds.
The seal ring is coupled to one shroud and extends from an outer surface of the shroud ring. The seal ring has a substantially cylindrical shape and is sized to provide a minimal clearance between an internal air deflector and the seal ring to minimize the flow of air through a space between the shroud ring and the air deflector.
At least one cooling fan cools an electric motor by drawing air from an air cooler air plenum through air pathways and directing the air into air passages extending through the motor rotor core and stator. The air removes heat from the rotor core and the stator core as it flows through the air passages and air plenums above and below the rotor and stator cores. The air then enters into an air cooler to be cooled and is discharged back into the air cooler air plenum. The seal ring prevents air from exiting the air plenum through a gap between the air deflector and the cooling fan. Without the seal ring, air enters the plenum and a portion of the air exits through the gap and then recirculates back to the fan intake. This recirculated air is not cooled because it does not pass through the air cooler. The recirculated air increases the temperature of the cooling air entering the rotor core and stator air passages and lowers the cooling efficiency of the cooling air and causes the motor to operate at increased temperatures. Operation at elevated temperatures causes premature failure of stator and/or rotor core windings.
The above described seal rings attached to electric motor cooling fans reduce internal air recirculation and increases cooling of motor windings to prevent motor failures and increase motor reliability.